The cell division cycle (cdc) is a tightly regulated process. Centrosomes are the main microtubule organizing center (MTOC) in most animal cells. Aberrations in this process often lead to cell abnormality, resulting in cell death or possibly oncogenesis. A common feature of tumor cells is abnormal centrosome numbers. The broad goal of this research proposal is to understand how the centrosome matures, maintains proper integrity, and what genes regulate its activity and function. The specific aims are to study centrosomin (Cnn), a core centrosomal protein necessary for centrosomal function, by mapping its functional domains and identifying interacting partners. Another specific aim is to identify the Drosophila homologs of Centrin, a centriolar protein implicated in centrosome duplication. Identification of fly Centrin based on sequence similarity to mammalian and yeast Centrin, followed by mutant analysis and RNAi in cell culture, will permit functional studies of Centrin in the fly. An EMS mutagenesis screen will be performed to attain mutations in Centrin genes in vivo. Defining the functions of Centrosomin and Centrin will contribute to our understanding of centrosome function.